Conventional coal burning boilers include a furnace that has a hollow shape and that is installed vertically. In such boilers, a plurality of combustion burners are arranged on the furnace wall along the circumferential direction, in multiple steps in the vertical direction. Additionally, in these combustion burners, a fuel-air mixture of pulverized coal (fuel) obtained by crushing coal and primary air is supplied and, also, a high temperature secondary air is supplied. Flames are formed by blowing the fuel-air mixture and the secondary air into the furnace. Thus, combustion in the furnace is possible. Moreover, a flue is connected to an upper portion of the furnace, and a superheater, a reheater, a fuel economizer, and the like for collecting the heat of the exhaust gas are provided on the flue, and heat exchange between the exhaust gas produced by combustion in the furnace and water is carried out. Thus, steam can be generated.
Examples of such a combustion burner of a coal burning boiler include the technology in the Patent Documents described below. The combustion burners described in the Patent Documents include a fuel nozzle capable of blowing a fuel gas obtained by mixing pulverized coal and a primary air, and a secondary air nozzle capable of blowing a secondary air from outside the fuel nozzle. In these combustion burners, a flame stabilizer is provided on an axial center side of the leading end of the fuel nozzle and, as a result, the pulverized coal concentrated flow is made to collide with the flame stabilizer, thereby enabling stable, low NOx combustion in a wide load range.